The present invention relates to a ball poppet valve and in particular to a poppet valve that includes a control stem which along its longitudinal axis has a non-constant diameter.
Such ball poppet valves are generally known from the prior art and are employed as directional control valves or shutoff valves having a freely movable ball poppet as a shutoff element. Ball poppet valves are distinguished by simplicity of construction and a high degree of freedom from leakage and are therefore well suited to many applications.
FIG. 3 is a longitudinal section through a schematic depiction of a prior art ball poppet. Such a ball poppet valve comprises a valve body 1 in which there is made a cylindrical valve bore 3 that links an inlet 5 and an outlet 7 of the valve bore 3. At the inlet end the valve bore 3 opens into a valve aperture 9, which can be closed by a ball poppet 11. In order to provide heightened tightness or a required freedom from leakage, the valve bore 3 has at the inlet end a chamfer 13, which guarantees that ball poppet 11 seats in centered fashion on the valve aperture 9 and seals it in leak-free fashion. As a rule ball poppet valves are not pressure-balanced; that is, the pressure is higher at the inlet end than at the outlet end. Because of the higher pressure at the inlet end, the ball poppet 11 is pressed against the valve aperture 9; for this purpose, however, there can also be a compression spring 15 by whose spring force the ball poppet 11 is held on the valve aperture 9. For opening the valve there a control stem 17 is located in the valve bore 3, which adjoins the ball and is movable along its longitudinal axis X so that the ball poppet 11 can be lifted off the valve aperture 9 by a force directed toward the ball poppet 11. The control stem 17 can be fashioned for example as the armature of an electromagnetic actuating unit (not shown) so that the valve opens or closes in dependence on the current flowing through a coil of the actuating unit.
A maximal annular flow area Amax is bounded by the control stem 17 disposed in the valve bore 3. This maximal flow area Amax depends on the radius R of the valve bore 3 and the radius r of the control stem 17 and is correspondingly calculated as the difference in cross-sectional area between the valve bore 3 and the control stem 17 according to equation 1 as follows:Amax=(R2−r2)π  (1)wherein R is the radius of the valve bore 3, r is the radius of the control stem 17 and π is the ratio of the circumference of a circle to its diameter.
In a ball poppet valve according to the prior art, control action is achieved in that an annular flow area A released between the ball poppet 11 and a control edge 19 on the valve aperture by lifting of the control stem 17 is smaller than the maximal flow area Amax bounded by the control stem 17 and the valve bore 3. Only an inadequate control action can be achieved with ball poppet valves according to the prior art, however, because this flow area A between the ball poppet 11 and the control edge 19 attains the maximal flow area Amax when the ball poppet 11 is lifted even very slightly.
A problem with ball poppet valves known from the prior art is that, because of their structural form, they enable a relatively large flow when the ball poppet is lifted even a relatively small amount off the valve aperture. Electromagnetically actuated ball poppet valves for example exhibit a large flow for even a small current flowing in an exciter coil. In electromagnetically controlled ball poppet valves of the kind identified above, this relationship manifests itself in a steep Q-I characteristic (flow-current characteristic) and has the disadvantage that only slight control of the flow is possible with such a ball poppet valve.
Gate valves are also known wherein the ports are connected to or separated from one another by a sliding element, the so-called gate. The movement of the gate here can be axial or rotational, a flow control action being achieved with individual chambers or channels. Gate valves are characterized by good control behavior and, in the example of electromagnetic actuation, by a flat Q-I characteristic. Such gate valves have the disadvantage that 100% freedom from leakage cannot be achieved because of manufacturing tolerances and the functional construction of the valves.
Also known from the prior art, for example from U.S. Pat. No. 6,418,967, are pressure control valves wherein the inflow or outflow behavior of a medium through a valve aperture is controlled by conical control elements. These valves also have the disadvantage that the conical elements employed therein do not ensure complete freedom from leakage.
There is a need for a ball poppet valve that exhibits both a high degree of freedom from leakage and a configurable control characteristic. In the case of electromagnetically actuated ball poppet valves in particular, the flow-current characteristic should be adjustable over a wide range.